Photodetectors using semiconductors (e.g., photodiodes and image sensors) are mounted on many apparatuses such as illuminance sensors, digital cameras, video cameras, monitor cameras, photocopiers, and facsimile equipment. Such photodetectors have a P-N junction structure using a P-type semiconductor and an N-type semiconductor, or a P-I-N structure in which an I layer having a low impurity concentration is interposed between a P-type and an N-type. A reverse bias is applied to the P-N junction or the P-I-N structure, to generate a depletion layer. Illuminating the depletion layer with light causes generation of photoelectrons by photoelectric conversion. The generation of the photoelectrons increases a drift current, detection of which allows for detection of the light. Furthermore, so-called CMOS type solid-state imaging elements are in wide use, in which the photodiodes as mentioned above are disposed in an array, and are manufactured by CMOS (Complementary Metal Oxide Semiconductor) processes, together with peripheral circuits (for example, refer to PTL 1).